--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/source/fitz/crypt-arc4.c	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,104 @@
+/* This code illustrates a sample implementation
+ * of the Arcfour algorithm
+ * Copyright (c) April 29, 1997 Kalle Kaukonen.
+ * All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that this copyright
+ * notice and disclaimer are retained.
+ *
+ * THIS SOFTWARE IS PROVIDED BY KALLE KAUKONEN AND CONTRIBUTORS ``AS
+ * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KALLE
+ * KAUKONEN OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "mupdf/fitz.h"
+#include <string.h>
+
+void
+fz_arc4_init(fz_arc4 *arc4, const unsigned char *key, size_t keylen)
+{
+	unsigned int t, u;
+	size_t keyindex;
+	unsigned int stateindex;
+	unsigned char *state;
+	unsigned int counter;
+
+	state = arc4->state;
+
+	arc4->x = 0;
+	arc4->y = 0;
+
+	for (counter = 0; counter < 256; counter++)
+	{
+		state[counter] = counter;
+	}
+
+	keyindex = 0;
+	stateindex = 0;
+
+	for (counter = 0; counter < 256; counter++)
+	{
+		t = state[counter];
+		stateindex = (stateindex + key[keyindex] + t) & 0xff;
+		u = state[stateindex];
+
+		state[stateindex] = t;
+		state[counter] = u;
+
+		if (++keyindex >= keylen)
+		{
+			keyindex = 0;
+		}
+	}
+}
+
+static unsigned char
+fz_arc4_next(fz_arc4 *arc4)
+{
+	unsigned int x;
+	unsigned int y;
+	unsigned int sx, sy;
+	unsigned char *state;
+
+	state = arc4->state;
+
+	x = (arc4->x + 1) & 0xff;
+	sx = state[x];
+	y = (sx + arc4->y) & 0xff;
+	sy = state[y];
+
+	arc4->x = x;
+	arc4->y = y;
+
+	state[y] = sx;
+	state[x] = sy;
+
+	return state[(sx + sy) & 0xff];
+}
+
+void
+fz_arc4_encrypt(fz_arc4 *arc4, unsigned char *dest, const unsigned char *src, size_t len)
+{
+	size_t i;
+	for (i = 0; i < len; i++)
+	{
+		unsigned char x;
+		x = fz_arc4_next(arc4);
+		dest[i] = src[i] ^ x;
+	}
+}
+
+void fz_arc4_final(fz_arc4 *state)
+{
+	memset(state, 0, sizeof(*state));
+}